Space Elevator

Good post Bill.

"Bill Daniels" wrote snip

One problem with the glider carrier aircraft concept is that a sailplane
configuration has a low MMO - probably no more than .5 Mach. (Research the
Perlan high altitude pressurized sailplane project.) On the other hand, a
supersonic or transonic airframe will have a much lower L/D.

Well, in the magic kingdom of drafting tables and simulators, we can
keep that 200 ft glider wing (100 per side) swept until the 747 tow
ship levels at FL500 straight and level, puts out flaps 10
electrically (since it's outside the 20,000 ft hydro flap limitation,)
slows to 150kts CAS/IND (a wag of just above VsFo 10 stall at altitude
since I can't find that chart,) and releases the still semi-swept
OrbitOne+glider wing assembly "cocoon" vehicle along it's tether line.
OrbitOne+glider then ‘unsweeps' going into high aspect ratio mode
pulling up with authority to avoid exceeding Vne/MMo of say .5 Mach.
The payout winch will spit out enough line to make up for the
difference in speed of the two vehicles. Then at when OrbitOne
reaches FL750, OrbitOne sheds its glider cocoon, and 747Towship goes
into a 30 degree bank to achieve max slingshot speed before
intentional release or line failure, whichever occurs first! Then,
OrbitOne lights the candle for Orbital Insertion.

There, I feel better. Burt and shareholders split up the 15 million
dollar profit.

Then we all live happily ever after.


Another problem is that aeroelastic flutter is proportional to true airspeed
so the Vne, expressed as IAS, will be lower at extreme altitudes unless
strong measures are taken to contain flutter. High aspect ratio
sailplane-like wings are prone to flutter.

The idea still has merit if the payoff sought is merely altitude and you can
accept low speeds. The airtow/winch launch approach could get a booster to
70 - 80 thousand feet fairly cheaply by keeping the tow aircraft lower in
the atmosphere where the engines produce more thrust - and the towing TAS
can be kept low to match the needs of the sailplane carrier aircraft at high
altitude.

Exactly.


One need take care that the pull on the tow line doesn't upset the towing
aircraft. If the tow line is long enough, the sag will have the pull vector
at the tug nearly horizontal.

Man, you're full of all kinds of good news. So the Russian AN-124
with dual tails may be better suited to prevent cable/tail fouling
after all.


Notwithstanding the above, you probably wouldn't encounter any problems
finding glider pilots willing to take the ride.

All-in-all, I'm inclined to think that a flyback, air-breathing first stage
ala Scaled Composites "White Knight" is the best solution. There is no
reason to think that it couldn't deliver a second stage booster to the same
altitude and airspeed as the winch launch method could. It would be
operationally simpler too.

Bill Daniels

You're probably right Bill. But "Big Fans" and "smooth bores" that
I'm familiar with, piddle out in the 40's – Low 50's even at the low
transport weights were talking about here. So I'm not sure how you
would deliver a second stage booster to the same altitude and airspeed
as the winch method could. Unless you built a massive U-2 ("Black
Knight"?) with ten U-2 turbojet engines (as opposed to high-bypass
turbofan engines) designed for those altitudes? I'm not sure you'd
have large money-making payload capabilities beyond the carrier ship
though since the air's so thin. Even though you have plenty of excess
thrust to get up there with your Black Knight/OrbitOne combo, the
wing's operating in a five knot speed range empty. Even a little
weight increase beyond the empty weight, pilot and fuel of the carrier
may exceed buffet boundries at 75,000ft and put you into a Gary Powers
high dive. Incidentally, he was not shot down. They were shooting at
him, but he panicked and broke out of the five knot range . The
tumble flamed out the engine. After he recovered much lower, but not
low enough to be in the relight envelope, the battery on the ADI was
only good for three minutes at the time, he knew it, and tried to get
out of Russian airspace. Three minutes later, right on schedule, the
battery croaked, the ADI (attitude directional indicator) went "tits
up" along with his nav, so all he had was airspeed and the sun on his
wingtip for directional reference to try and get back to friendly real
estate. But he was concentrating so much on the wingtip that he
punched through VNE and tore the tail off, and... the rest is history.

(Another old roommate who flew tst for most of his career told me the
U-2 is the hardest plane he's ever flown.) That's the beauty of
having a towship down in the thicker air. Omitting the heavy engines
at FL750 can equate to more second stage oxidizer for Orbit riding on
the same size wing. That's assuming we don't tear our line apart from
all the drag. Feel free to argue for a Black Knight type solution
though, since, as you correctly pointed out: it is a lot simpler!

BTW hope you guys enjoyed my "fictional" U-2 story above.

pacplyer